A wide variety of coatings can be applied to glass sheets and other sheet-like substrates to provide the substrates with desired properties and characteristics. Well known coating types include low-emissivity coatings, solar control coatings, hydrophilic coatings, hydrophobic coatings, photocatalytic coatings, photovoltaic coatings, electrochromic coatings, mirror coatings, and antireflective coatings. In some cases, it is desirable to apply coatings to both sides of a sheet-like substrate. For example, a substrate may be provided with a low-emissivity coating on one side and a photocatalytic coating on the other side. Alternatively, a substrate may be provided with a low-emissivity coating on one side and a hydrophobic coating on the other side. Further, a substrate may be provided with a low-emissivity coating on one side and a hydrophilic coating (which may or may not be photocatalytic) on the other side. Still further, a substrate may be provided with a photocatalytic coating on one side and a mirror coating on the other side. Many further variants are possible.
When coatings are applied to both sides of a substrate, the coating deposition can be performed, for example, using a coater that is adapted only for downward deposition (e.g., using a coater adapted only for conventional downward sputtering). This can involve applying a coating to one side of the substrate in a first pass through the coater, and thereafter applying another coating to the other side of the substrate in a second pass through the coater, flipping the substrate between the first and second passes. Alternatively, one side of a substrate can be coated by conveying the substrate through a first coater (e.g., a coater adapted for pyrolytic deposition), and the other side of the substrate can be coated by subsequently conveying the substrate through a second coater (e.g., a coater adapted for sputter deposition). Such processes, however, are less than ideal in terms of efficiency and simplicity.
Attempts have been made to provide more efficient methods for coating both sides of a sheet-like substrate, generally by coating both sides of the substrate in a single pass through a single coating apparatus. Reference is made to U.S. Pat. No. 5,683,561 (Hollars et al.) and U.S. Pat. No. 5,762,674 (Maltby, Jr. et al.), the entire contents of each of which are incorporated herein by reference. Particularly useful technology for coating both sides of a substrate is disclosed in International Patent Application PCT/US99/02208 (International Publication No. WO 00/37377 (Bond et al.)), the entire contents of which are incorporated herein by reference.
While these recent technologies show great improvement over traditional methods, there is a need for other sophisticated technologies in which coatings are applied to both sides of a substrate. For example, with the rapid evolution of new coatings and ongoing advances in deposition equipment, there is a need for other efficient methods in which both sides of a substrate can be coated with high quality coatings. There is a particular need for technology in which both sides of a large-area substrate can be provided with pinhole-free coatings. This is especially true with respect to glass sheets and other large-area substrates designed for architectural and automotive glass applications.